Tube swaging, for example, where a collar is swaged into the end of a tube, requires a mandrel in a roller swage tool to be rotated until a predetermined torque is obtained. For such swaging, the required accuracy is 5% over torque ranges from 190 to 2300 inch pounds and 10% in ranges from 6 to 190 inch pounds.
Prior methods used to perform this type of swaging are indicated in the following:
In manual operation, an operator uses torque wrenches having various ranges depending upon tube sizes. This method is too time consuming to be practical.
Air motors have been used to drive a mandrel until the motor stalls. The air pressure is preset to a value corresponding to a desired stall torque. This method is inaccurate because friction losses in the motor affect the final output torque. For the ranges indicated above, several sizes of air motors are required to limit inaccuracies to a sufficiently low level and this type of operation requires several interruptions for changes of motors.
Electrical drill motors have been used to provide the power and the current to the motor is sensed and compared to a preset value. As the torque increases, the current will increase and an electronic circuit breaks the power to the motor when the preset value is reached. One problem with this system is that current is not an accurate measure of motor torque because of friction losses, and another problem is that when a motor is turned off, it continues to coast because of the energy stored in the rotating inertia of its rotor. Two sizes of drill motors are required to keep the errors reasonably small for the above torque ranges, but the system could not be made to meet the tolerance requirements.
Hydraulic systems have been tried but they suffer from the same type of errors as pneumatic systems.
A search of the patent literature has disclosed the following patents of interest.
U.S. Pat. No. 2,535,782 to Carlson discloses a power driven roller tube expander, a mandrel revolution counter driven by a power device, and means adapted to be actuated as a result of an increase in the power, the revolution counter being arranged to stop rotation of the mandrel when a predetermined number of subsequent revolutions has been counted.
U.S. Pat. No. 3,494,430 to Lehmann et al discloses means for measuring reactive torque on a casing during rotation of a driven element therein, whereby a motor in the casing is reversed and shut off by control means responsive to reactive torque on the casing.
U.S. Pat. No. 4,106,570 to Eshghy et al describes an air-power tool including a motor, a gear reducer and a driver in which the motor turns at a higher rate than the driver. An angle sensor is arranged to determine rotation of the motor rather than of the driver. Means are provided to compensate for the rotation sensing as a function of applied torque.
U.S. Pat. No. 4,126,818 to Taylor discloses a method for driving an output shaft through a steplike angular displacement in which a command signal is used to energize a stepper-type primary motor connected to drive an output shaft so as to develop reaction torque by means of the stepper-type primary motor, transducing the reaction torque into a control signal and using the signal to energize a secondary motor which is connected in driving relation to the output shaft, thereby energizing the secondary motor when reaction torque is present to augment torque produced by the stepper-type primary motor to drive the output shaft.
The following patents of general interest were also found:
U.S. Pat. No. 1,859,814: R. D. Wyckoff PA1 U.S. Pat. No. 1,904,765: W. L. Hawk PA1 U.S. Pat. No. 2,725,918: W. B. Deshler PA1 U.S. Pat. No. 3,013,600: R. E. Baker et al. PA1 U.S. Pat. No. 3,693,726: Hornig et al. PA1 U.S. Pat. No. 3,926,264: Bardwell et al. PA1 U.S. Pat. No. 3,939,920: Hardiman et al. PA1 U.S. Pat. No. 3,973,434: S. K. Smith PA1 U.S. Pat. No. 3,975,954: R. G. Barnich PA1 U.S. Pat. No. 4,104,778: W. C. Vliet PA1 U.S. Pat. No. 4,104,779: J. A. Sigmund PA1 U.S. Pat. No. 4,106,176: Rice et al. PA1 U.S. Pat. No. 4,126,818: W. W. Taylor PA1 U.S. Pat. No. 4,198,737: S. Eshghy PA1 U.S. Pat. No. 4,418,765: Mori et al. PA1 Russian Pat. No. 377,949